Oxidation is one of the most fundamental transformations in organic chemistry. Oxygenation of allylalkane or alkylarenes to the corresponding carbonyl compounds is an important reaction because an oxygen atom can be introduced into organic substrates. Conventionally, stoichiometric amount of an oxidant such as manganese dioxide, chromic acid, potassium dichromate, silver oxide, selenium dioxide and periodic acid have been employed, which suffer from the drawback that they produce environmentally unacceptable heavy metal wastes. An attractive option is the development of methods using molecular oxygen or air, especially from the perspective of atom efficiency and environmental concerns.
Recently, considerable progress has been made towards realizing the goal of using atmospheric oxygen for oxidation including Mukaiyama's oxidation-reduction-hydration reaction using several transition metal catalysts. Therefore, to improve yields, metal catalysts or photo-activation are employed to achieve the desired goal, but inviting environmental concerns.
Oxidative cleavage of the carbon-carbon double bond of substituted styrene derivatives to afford the corresponding ketones under an atmospheric pressure of molecular oxygen without the use of transition metal catalysts or photo-activation and oxidation of fluorine derivatives at the benzylic position to the corresponding carbonyl compounds using molecular oxygen promoted by activated carbon are reported in the literature.
So, a metal free oxidative process to obtain these vital constituent is an unaddressed need in the art, such that the process is not only green, but also results in the desired product in substantial yields.
Article titled, “Metal-Free Allylic Oxidation with Molecular Oxygen Catalyzed by g-C3N4 and N-Hydroxyphthalimide” by Guiyin Liu•Ruiren Tang•Zhen Wang in Catal Lett (2014) 144:717-722 reports a Polymeric graphitic carbon nitride (g-C3N4) is a layered graphite-like nitrogen-rich material (as a base), bearing the potential ability to reductively adsorb molecular oxygen for catalytic allylic oxidation. It provides a strategy for employing such nitride-rich g-C3N4 combined with NHPI to form an all organic metal-free composite and have examined its activity for allylic oxidation with molecular oxygen as the primary terminal oxidant. Furthermore, N-hydroxyphthalimide(NHPI) has been recognized as an efficient catalyst for aerobic oxidation of various organic compounds like cyclohexene under mild conditions (solvent is polar ex: acetonitrile) in the presence of various co-catalysts. It reports >74% conversion and >40% selectivity.
Article titled, “Allylic and benzylic oxidation reactions with sodium chlorite” by Samuel M. Silvestre, Jorge A. R. Salvador in Tetrahedron Volume 63, Issue 11, 12 Mar. 2007, Pages 2439-244 reports that various allylic and benzylic substrates were selectively oxidized to the corresponding enones in good yields using sodium chlorite, either in combination with tert-butyl hydroperoxide in stoichiometric conditions, or associated with N-hydroxyphthalimide as catalyst. These oxidation reactions were effectively and economically performed under mild, transition-metal free conditions and therefore the dual challenge of cost effectiveness and benign nature of the processes was met with.

Article titled, “Highly efficient and metal-free oxidation of olefins by molecular oxygen under mild conditions” by Xinli Tong, Jie Xu in Tetrahedron Volume 63, Issue 32, 6 Aug. 2007, Pages 7634-7639 reports a Highly efficient and metal-free aerobic oxidations of cyclohexene and styrene performed under mild conditions in the presence of 1,4-diamino-2,3-dichloro-anthraquinone and N-hydroxyphthalimide. When cyclohexene was oxidized, an 89% conversion and 71% selectivity for 2-cyclohexen-1-one was obtained under 0.3 MPa at 80° C. for 5 h. Furthermore, more olefins were efficiently oxidized to corresponding oxygenated products under mild conditions.
Article titled, “Selective Allylic Oxidation of Cyclohexene Catalyzed by Nitrogen-Doped Carbon Nanotubes” by Yonghai Cao, Hao Yu, Feng Peng and Hongjuan Wang in ACS Catal., 2014, 4 (5), pp 1617-1625 reports Carbon nanotubes (CNTs) and nitrogen-doped CNTs (NCNTs) as metal-free catalysts in the selective allylic oxidation of cyclohexene using molecular oxygen as oxidant in the liquid phase. High cyclohexene conversion (up to 59.0%) and 620.1 mmol g−1 h−1 mass-normalized activities were obtained for NCNTs.
Article titled, “Copper-Catalyzed Allylic Oxidation of Cyclohexene with Molecular Oxygen” by Xu Zhang, Rong Yi, Tian Chen, Shichun Ni, Genlin Wang, Lei Yu in Scientific Journal of Frontier Chemical Development June 2013, Volume 3, Issue 2, PP. 25-29 reports a Copper-catalyzed aerobic allylic oxidation of cyclohexene under solvent-free conditions leads to 2-cyclohexenol and 2-cyclohexenone. This pathway is suitable for industrial production, owing to the high conversion rate and selectivity, the solvent-free conditions, the cheap catalyst and the environment-friendly oxidant and procedure.
Article titled, “Allylic Oxidation of Cyclohexene with Molecular Oxygen Using Cobalt Resinate as Catalyst” by Caixia Yin, Zehui Yang, Bin Li, Fengmei Zhang, Jiaqiang Wang, Encai Ou in Catalysis Letters 01/2009; 131(3):440-443 reports that Allylic oxidation of cychohexene under atmospheric pressure of molecular oxygen was carried out over cobalt resinate in the absence of solvent. It was shown that cobalt resinate exhibited promising catalytic activity for the oxidation of cyclohexene to 2-cyclohexen-1-ol and 2-cychohexen-1-one under mild condition.
Article titled, “Metal-free allylic/benzylic oxidation strategies with molecular oxygen: recent advances and future prospects” by Kexian Chen in Green Chem., 2014, 16, 2344-2374 reports the selective oxo-functionalization of hydrocarbons under mild conditions with molecular oxygen as the terminal oxidant continues to be a hot topic in organic synthesis and industrial chemistry. This critical review summarizes recent significant advances achieved in this important field under the scope of green chemistry, which covers the promising applications and brief mechanistic profiles involving three kinds of efficient catalysts, namely N-hydroxyimides, homogeneous/heterogeneous light-sensitive molecules, and heteroatom-doped carbon materials, and concerns the sustainability of these methods.
Thus, there is a need in the art to provide processes for oxidation that effectively and efficiently employs atmospheric oxygen as an oxidant without affecting yield or desired product.
The process of the present invention overcomes several of the drawbacks of the prior art and provides an alternate to the processes which involved usage of unacceptable heavy metals or transition metals. The present process is green/eco-friendly, convenient, economical and offers other advantages like easily available starting materials, high yield and selectivity.